Paper products have a wide variety of applications for food applications. Paper, solid board and molded pulp can be engineered to create cups, plates, sandwich wraps, butcher paper, freezer wraps and food containers such as French fry holders and sandwich clamshells. In order for the paper products to perform for their intended applications, a barrier coating must be applied to guard against any potential permeability of water, oil, or grease from aqueous or non-aqueous sources. If moisture (liquid or vapour) permeates the paper, the paper loses its rigidity and its performance as a package decreases significantly. In addition, the moisture will cause a “cockling” of the paper, causing point-of-sale graphics to lose their appeal. If oil or grease comes in contact with the paper, it will cause staining on the packaging which is unappealing for two reasons: (1) the fat stains give the purchaser the impression that the food is not healthy because of its fat content; and (2) the package looks “dirty” and becomes difficult to sell.
Paper coatings are generally made from pigments, binders, film formers and various additives intended to achieve desired performance characteristics. In many instances the coating process is divided into two distinct steps: the application of a base coat and the application of a top coat. The base coat typically comprises chemical formulations that decrease the cellulosic substrate's porosity and may improve the adhesion of the subsequent topcoat. The top coat is generally formulated with the focus on the desired barrier properties of the specific application, for example, water, grease and/or oil resistance.
It is well known in the art to apply chemical formulations that include fluorochemicals, often containing chemicals such as perfluorooctanoic acid (PFOA), wax or polyethylene to cellulosic substrates to impart grease and oil resistance to the substrate. Although these chemical applications provide the application performance desired, they are subject to environmental and safety concerns. Specifically, the PFOA-containing materials include halogenated hydrocarbons that have been demonstrated to accumulate in fats of living beings and do not biodegrade readily. Examples of halogenated hydrocarbons include but are by no means limited to polychlorinated biphenyl (PCB), dichlorodiphenyltrichloroethane (DDT) and polyvinyl chloride (PVC). Waxes and polyethylene are hydrocarbon-based and, when laminated or extruded to packaging, make these materials non-recyclable. For polyethylene, this is because the polyethylene film does not easily separate from the substrate, causing clumps of materials to build up onto the pulp screen during the paper recycling process. For wax, the high temperatures that are used during the recycling process cause the wax to melt. The wax then deposits on parts of the machinery, causing a decrease in efficiency and resulting in spotting to the recycled paper, which often results in the recycled paper having to be sold as inferior quality. This inferior paper is often sold at a discounted of between 15%-20% from a premium quality recycled paper.
It is accepted in the art to coat paper and paperboard with wax and polymer coatings such as polyethylene, acrylic polymers, ethylene-vinyl acetate copolymers and conventional rubber type polymers such as styrene-butadiene polymers. These formulations provide coatings that are useful for providing resistance to water and oil and/or grease penetration to paper, paperboard and corrugated products. However, these products, are difficult to recycle and do not provide repulping characteristics required for reuse in the paper making process, as discussed above.
Therefore, the need exists for chemical formulations for paper coatings that are water, oil and/or grease resistant, and are environmentally friendly without possible health risks. Specifically, it would be quite useful for such formulations to be engineered for food applications such as wrappers, assorted packaging and containers where food contact is imminent.